When a fire claims one of their own, there's plenty of guilt and blame to go around. Lt. Matthew Casey, in charge of the Truck, tries to carry on, but butts heads with the brash Lt. Kelly Severide of the Rescue Squad - and each blames the other for their fallen team member. The firehouse also includes: Battalion Chief Wallace Boden, a fireman's fireman who is confronted by important personal decisions; paramedics Gabriela Dawson and Leslie Shay, who share a close bond and team together to face some of the most harrowing situations imaginable; Peter Mills, an academy graduate who is the latest generation in a family of firefighters; and Christopher Herrmann, a seasoned veteran who loses his home to foreclosure and now must uproot his family to move in with his in-laws.

Severide is hiding a serious shoulder injury sustained in the fire that killed Andy Darden, and grapples with his guilt as he fights to rescue a construction worker trapped in a building collapse. Adding to the burden, Darden's wife Heather turns on Severide at the annual firefighters' barbecue, blaming him for her husband's death. A call is made to an accident site at Hancock Tower, where two teenagers are pinned in a vehicle trapped beneath the falling debris of a broken window washer's cart. Meanwhile, Casey and Hallie work to figure out their future together.

Everyone in the firehouse is ordered to take a drug test after a call to a daycare center exposes them to a makeshift meth lab, and Severide stalls, not wanting his injury, or the painkillers he takes, to be discovered. Meanwhile, Truck and Squad find themselves pinned down by gunfire while trying to help the victim of a gang shooting, and a deep-fried turkey fire grows from small to explosive when a garage catches fire. Elsewhere, Dawson saves a bleeding man and Casey delivers a baby on the scene of a massive car pileup on the freeway.

A troubled Chief Boden goes to the police when a man dies in a hardware store fire set by Ernie, the troubled teenage firebug he’s been trying to help, and his Uncle Ray. Meanwhile, Severide decides on his future and reaches out to his father. Elsewhere, Otis finds camaraderie when he fills in for a few shifts at the slowest firehouse in the city, and makes a decision of his own, while Dawson and Shay find themselves in a bad predicament during a call to a tenement.

An arsonist targets Lt. Severide. Meanwhile, Station 51 is under scrutiny by Gail McLeod, a financial consultant for the city who is deciding if any firehouses should be closed. Mouch receives a visit from his Japanese girlfriend, Lt. Casey "celebrates the one-year anniversary of Andy's death, and Shay suspects Severide's paternity.

While out on a jog, Severide comes across a secluded and empty construction site and encounters a young boy who has been trapped in a backhoe loader and is in dire need of assistance. Boden and McLeod continue to butt heads about the future of the firehouse and Boden breaks news about his future to Casey. Meanwhile, it's election day for the union presidency and Mouch and Greg Sullivan have a debate on Otis' podcast. With rival bar Game Day's future in peril, the finger is being pointed at Molly's.

All seems lost with firehouse 51 on the verge of closing its’ doors, thanks in no small part to Gail McLeod, but Chief Boden and the rest of the house refuse to allow themselves to sit by and let it happen. An emergency call to an apartment structure fire tests everyone’s limits and puts the squad in harm’s way. Meanwhile, Dawson receives some life-changing news and union president Greg Sullivan makes headlines, which has an immediate impact on Mouch.

When a drunk driver knocks down a transformer, the entire neighborhood is left without power on a frigid Chicago night and members of Firehouse 51 step up to lend their much needed help. While many from the community ride out the night at the station, in the midst of such close quarters, romances speed up and tempers flare. Meanwhile, Casey continues to lie to both himself and Dawson about his condition and the stakeholders in Molly's bicker about the bar's direction.

A fire at a boarding school leaves Lt. Severide shaken and wondering if he could have done more. Meanwhile, with the firehouse in full support of Dawson as she retakes the fireman’s exam, Lt. Casey attempts some political maneuverings on her behalf. Elsewhere, Mills looks for answers about his father’s mysterious past and Chief Boden’s grand plans take a detour.

Boden forces members of Firehouse 51 to pull themselves back together in the aftermath of a harrowing fire explosion. While Severide goes missing for one week too many, Casey works to track down his whereabouts. Newhouse brings some unexpected news regarding one of Mills’ relatives. Herrmann and Otis make some new goals regarding Molly’s.

The members of the firehouse spring into action when a helicopter explodes over a populated area.

A house fire sees the team attempting to save the lives of a couple trapped inside. Chief Boden prepares to start his new family. The combination of life at work and home sees Casey and Dawson drifting apart.

Lt. Casey puts his life on the line and digs deeper into the shady dealings of Jack Nesbitt. Chief Boden must figure out how to create unity in a divided house, while Severide comes to question his own judgment. A dangerous warehouse blaze quickly gets out of control and threatens members of firehouse 51.

Patterson fills in for Boden, who's trying to clear his name. Severide learns where Serena may be hiding. Herrmann and Otis give Freddie a job that keeps him close by. Jimmy and Chili draw more attention then either bargained for.

Casey reconsiders his run for alderman after he's targeted by a propaganda campaign. The squad responds when a man is trapped inside of a burning car. Trudy's nerdy brother plans Mouch's bachelor party. Jimmy and Brett investigate a kidnapping on their own.

Severide and Stella search for Grant, who's AWOL from Chicago Med. Dawson questions her career path. Casey's relationship with his political consultant cools. Borrelli's anger at Boden over his brother's death boils over. Mouch and Brett partner on a new venture.

Lt. Casey and Dawson apply for permanent adoption of Louie, but quickly discover a hurdle. Firefighter-turned-medical student Jeff Clarke approaches Lt. Severide with an interesting proposition. With hopes of reinvigorating business at the bar, Otis convinces a skeptical Herrmann to throw a bash in celebration of the milestone 100th anniversary of Molly's, but not without complications.

After exercising his disdain and authority over Chief Boden, Chief Anderson reassigns members of 51 to various houses around town, citing the need for improvement. The ramifications are felt by the crew, who are left to make the best of their respective situations in their new surroundings.

Casey discovers a new crack house on the block that is harboring a female junkie. Dawson and Brett get assigned a new trainee for the shift. Meanwhile, Severide gets an unexpected visit from his father and Herrmann deals with family issues when his son gets into trouble at school.

A dangerous warehouse fire puts truck and squad at risk. Tensions are high for Dawson and Casey when Dawson's father overstays his welcome at their home. Meanwhile, Casey continues to fight for his first responders bill, Mouch makes a serious decision regarding his future and Herrmann goes to tremendous lengths to make a young boy smile.

With most of the squad still trapped inside the burning warehouse fire, Chief Boden makes a risky last-minute decision in an effort to save his men. Dawson continues to deal with her father, who has new plans for himself. Brett's childhood friend Hope visits the Windy City and strikes the attention of someone within the firehouse, while Kidd goes head-to-head with her landlord. Meanwhile, a fire at a high school hits close to home for Boden.

After heroically saving a mother and newborn baby from a rooftop fire, Kidd receives surprising news when she discovers she is being transferred out of the firehouse. Severide and Casey believe something is off about the turn of events, prompting them to investigate the situation. Otis and Herrmann discuss the possibilities of taking over a rundown bar and Dawson's frustration with her father, Ramon, reaches a boiling point.

After learning unsettling news, Dawson enlists Severide to help her out. Elsewhere, Casey and Dawson struggle with communication issues while Brett and Kidd compete to win the heart of Zach, a Hazmat officer. Meanwhile, Otis, Herrmann and Mouch are on a mission to locate the source of a horrible stench that is making life unpleasant at Firehouse 51.

While working to track down a bombing suspect, Voight and Antonio meet with Chief Boden, who unwillingly agrees to let Dawson and Brett go undercover. As the investigation continues, Boden, Casey and Severide lend their skilled expertise in the investigation. Elsewhere, Kidd and Zach's relationship hits a bump and Cruz has a hard time expressing his true feelings for Brett. Meanwhile, Herrmann and Connie are forced to come up with an alternative solution when two birthday parties are booked on the same day at the firehouse.

The crossover starts on Chicago Fire S05E016 Profiles (I).

After responding to a car accident, Casey and Dawson become skeptical when a domineering husband continues to answer for his injured wife. Cruz becomes frustrated with Herrmann and Mouch when he discovers they have contacted people regarding his "Slamigan" invention without his knowledge. Kidd uncovers something meaningful and important to Severide while Brett discovers some potentially unsettling news.

After saving a girl from a car accident, Chief Boden and Lt. Severide are taken aback when they receive a surprise package. Brett struggles to keep quiet about Cruz reacquainting with his now-married high school sweetheart and Otis tackles his next challenge. A crisis brings Bria back into Dawson's life.

Boden's chances for a promotion are met with potential complications. Dawson and Casey don't see eye to eye on an important decision, while Kidd finds herself struggling to find time with Severide. Brett and Dawson respond to a tough call that quickly turns dangerous.

Casey tries to deal with his unsettled personal life and the firehouse welcomes a new member. Boden clashes with new Assistant Deputy Commissioner Jerry Gorsch.

Stakes are high when a massive car pile-up on the freeway impacts someone dear to the firehouse family. Brett and Foster encounter a harrowing call while Kidd and Severide find their relationship being tested.

Brett, Foster and Kidd take a road trip to Indiana and encounter an accident involving a boys' hockey team that leaves them scrambling and relying on their instincts to save the injured. The rest of Firehouse 51 competes in the annual chili cook-off.

Tensions run high between Casey and Herrmann after the firehouse responds to an apartment complex fire. After discovering something extremely suspicious during the call, Kidd and Severide do some investigating and get CPD on the case.

Severide and Kidd continue to investigate Benny’s old arson case, unexpected news leads Brett to ponder a big decision and all hell breaks loose.

The mattress factory fire spirals out of control. Truck and squad lay it on the line in hopes of getting the trapped victims out alive.

A rare but deadly bacteria takes its toll on numerous victims around the city, leaving Chicago’s finest first responders to work together alongside the CDC to resolve the dangerous situation. Following a fire at a local university that ties into the outbreak, Severide has suspicions that something bigger is happening.

The crossover continues on Chicago Med S05E04 Infection, Part II (II) and Chicago P.D. S07S04 Infection, Part III (III).

An unexpected visit throws Casey for a loop. Severide sets out to exonerate a wrongly convicted arsonist. Kidd pays the price for burning the candle at both ends. Cruz goes on a mission to fix one of Otis’s old toys.

The surprising arrival of a new fire truck brings both joy and chaos to members of Firehouse 51. Boden and Severide are asked to make peace with an old foe for the greater good. Brett receives family news while Foster plans a party with friends.

Things get personal for Casey and Gallo in the aftermath of a suburban house fire involving a mother and her young son. Herrmann campaigns for more respect. Kidd has an idea for giving back to her community.

Firehouse 51 welcomes a new member to the team, whose presence could provide some complications. Brett's leadership shines during a scary call. Boden sees great potential in Kidd and proposes an idea that could have lasting repercussions.

When Firehouse 51 is called to the scene of a dangerous blaze inside a 10-story storage unit, Herrmann and Cruz find themselves trapped inside a freight elevator with all communications cut off.

Mouch, Gallo, Ritter and Mackey report for training. A nasty blow to the head brings Casey unimaginable pain.

A mysterious caller who is in danger relies on Kidd to help save her and her brother. The firehouse helps Cruz get ready for fatherhood.

The firehouse reacts to some exciting news, a mysterious stranger arrives and a shocking call takes Severide's breath away.

Casey makes a life-altering decision. Gallo, Ritter and Violet agree to an interview and photo shoot. Brett and Mouch launch the paramedicine program. Cruz comes closer to fatherhood.

Gallo, Violet and Ritter debut their microbrewery business at Winterfest. Brett prepares to present her paramedicine program to an oversight panel. Firehouse 51 gets in the holiday spirit.

Firehouse 51 must band together when one of their own is taken hostage.

Kidd recruits Carver, Capp and Tony to help prepare her new lieutenant's quarters. Severide and Det. Pryma pair up to work a police investigation. Firehouse 51 fights a movie theater fire.